What is a wireless communication gateway
Wireless communication gateway is a gateway that uses wireless technology for transmission. It is widely used in vehicle monitoring, remote control, telemetry, small wireless networks, wireless meter reading, access control systems, community paging, industrial data collection systems, wireless tags, and identities. Identification, non-contact RF smart card, small wireless data terminal, fire safety system, wireless remote control system, biological signal network, hydrological and meteorological monitoring, robot control, wireless 232 data communication, wireless 485/422 data communication, digital audio, digital image transmission, etc. in the field. The gateway mainly consists of a transmitter, receiver and controller.
Wireless communication gateway varieties
Common wireless communication gateways on the market are divided into the following types:
1. Wireless data transmission gateway. This kind of gateway manufacturer has already made a single-chip microcomputer and has written the program of the wireless communication part. It can directly send and receive data through the serial port. It is simple to use, but the cost is relatively high.
2. The wireless transceiver gateway generally controls wireless transceiver data through a microcontroller, usually in FSK or GFSK modulation modes.
3. ASK superheterodyne gateway is mainly used for simple remote control and data transmission.
Things to note about wireless communication gateways
The wireless communication gateway must use signal modulation to work properly. Another important use of the wireless communication gateway is to cooperate with the microcontroller to complete data communication. At this time, there are certain skills:
1. Reasonable communication speed
The maximum transmission data rate of the data gateway is 9.6KBS, which is generally controlled around 2.5k. An excessively high data rate will reduce the reception sensitivity, increase the bit error rate, and even fail to work at all.
2. Reasonable information code pattern
When microcontrollers and gateways work, they usually define their own transmission protocols. No matter what modulation method is used, the information code format to be transmitted is very important, and it will directly affect the reliable sending and receiving of data.
Code group pattern recommendation plan
For the preamble synchronization code data frame, the preamble length should be large, so 10ms, to avoid background noise, because the first bit of data received by the receiving gateway is easily disturbed (i.e., zero-level interference), causing errors in the received data. Therefore, using CPU encoding and decoding can add some garbled characters before the data identification bits to suppress zero-level interference. Synchronization codes are mostly used to differentiate between preamble and data. It has certain characteristics so that the software can identify the synchronization code through a certain algorithm and be ready to receive the data.
Data frames should not use non-return-to-zero codes, let alone long 0 and long
1. Choose Manchester encoding or POCSAG code, etc.
3. Interference of microcontroller on receiving gateway
When the microcontroller simulates 2262, it is usually normal. However, when the microcontroller simulates 2272 decoding, it is usually found that the remote control distance is much shortened. This is because the multiplication of the clock frequency of the microcontroller will cause interference to the receiving gateway. The electromagnetic interference of the 51 series of microcontrollers is relatively large, and the 2051 is slightly smaller. Smaller, the PIC series is smaller, we should use some anti-interference methods to reduce interference. For example, the single-chip computer and the remote control recovery circuit are powered by two 5-volt power supplies respectively, and the recovery board is powered by a 78L05. The clock area of the single-chip computer is far away from the recovery gateway, which reduces the operating frequency of the single-chip computer and adds shielding in the middle.
When the wireless communication gateway interfaces with the 51 series microcontroller, it is best to make an isolation circuit, which can better prevent the electromagnetic interference of the microcontroller to the receiving gateway. When the wireless communication gateway is working, it usually outputs high-level pulses, not DC levels, so it cannot be tested with a multimeter. During debugging, a light-emitting diode can be connected in series with a 3K resistor to monitor the output status of the gateway. When using wireless data gateways and special codec chips such as PT2262/PT2272, the connection is very simple and only requires direct connection. The transmission distance is ideal and can generally reach more than 600 meters. If used in conjunction with a microcontroller or microcomputer, the microcontroller will be affected. Perhaps the clock of the microcomputer is disturbed, causing the transmission distance to be significantly reduced. Generally, the effective distance is within 200 meters.Keywords: remote measurement and control terminal